1. Technical Field
The present invention relates to a light-emitting element, a light-emitting device, a display, and electronic equipment.
2. Related Art
Organic electroluminescence elements (so-called organic EL elements) are light-emitting elements each having a structure in which at least one light-emitting organic layer is disposed between an anode and a cathode. In such a light-emitting element, by applying an electric field between the cathode and the anode, electrons are injected into the light-emitting layer from the cathode side, and holes are injected from the anode side. The electrons and the holes are recombined in the light-emitting layer to generate excitons, and energy when the excitons return to the ground state is emitted as light.
As such a light-emitting element, for example, one that has three light-emitting layers corresponding to three colors, R (red), G (green), and B (blue), are laminated between a cathode and an anode and emits white light is known (for example, see JP-A-2005-100921). This light-emitting element that emits white light can display a full color image by being used in a combination with three color filters of R (red), G (green), and B (blue) for the corresponding pixels.
In the light-emitting element disclosed in JP-A-2005-100921, an intermediate layer constituted of a hole-transporting material is disposed between light-emitting layers. This intermediate layer restricts the transportation of electrons from the light-emitting layer on the cathode side to the light-emitting layer on the anode side, and thereby each light-emitting layer is allowed to emit light in a balanced manner. In addition, such an intermediate layer efficiently transports holes from the light-emitting layer on the anode side to the light-emitting layer on the cathode side, and thereby the luminous efficiency of the light-emitting element can be enhanced.
However, in the light-emitting element according to the invention of JP-A-2005-100921, electrons accumulate near the interface between the intermediate layer and the light-emitting layer on the cathode side, which causes a problem that the light-emitting layer on the cathode side is deteriorated, resulting in a reduction in the lifetime of the light-emitting element.